bchFNBH bacteriochlorophyll synthesis genes of Rhodobacter capsulatus and identification of the third subunit of light-independent protochlorophyllide reductase in bacteria and plants

Abstract

We present the nucleotide and deduced amino acid sequences of four contiguous bacteriochlorophyll synthesis genes from Rhodobacter capsulatus. Three of these genes code for enzymes which catalyze reactions common to the chlorophyll synthesis pathway and therefore are likely to be found in plants and cyanobacteria as well. The pigments accumulated in strains with physically mapped transposon insertion mutations are analyzed by absorbance and fluorescence spectroscopy, allowing us to assign the genes as bchF, bchN, bchB, and bchH, in that order. bchF encodes a bacteriochlorophyll alpha-specific enzyme that adds water across the 2-vinyl group. The other three genes are required for portions of the pathway that are shared with chlorophyll synthesis, and they were expected to be common to both pathways. bchN and bchB are required for protochlorophyllide reduction in the dark (along with bchL), a reaction that has been observed in all major groups of photosynthetic organisms except angiosperms, where only the light-dependent reaction has been clearly established. The purple bacterial and plant enzymes show 35% identity between the amino acids coded by bchN and chlN (gidA) and 49% identity between the amino acids coded by bchL and chlL (frxC). Furthermore, bchB is 33% identical to ORF513 from the Marchantia polymorpha chloroplast. We present arguments in favor of the probable role of ORF513 (chlB) in protochlorophyllide reduction in the dark. The further similarities of all three subunits of protochlorophyllide reductase and the three subunits of chlorin reductase in bacteriochlorophyll synthesis suggest that the two reductase systems are derived from a common ancestor.

Cloning of a gene involved in rRNA precursor processing and 23S rRNA cleavage in Rhodobacter capsulatus

“…When RNA was isolated from wild-type strain 37b4, most of the 23S rRNA was cleaved to 1.6-kb (16S) and 1.3-kb (14S) rRNA species (Fig. 2) (6). The pRK290 (9) derivative carrying the EcoI fragment was named pRKEI.…”

Genetic evidence that PpsR from Rhodobacter sphaeroides 2.4.1 functions as a repressor of puc and bchF expression

“…sphaeroides, as well as in R. capsulatus, and for some time have been considered potential sites for repressor binding (2,4,15,17). In a gel shift assay, the bchC regulatory sequence from R. capsulatus, containing two such palindromes, was shown to interact with a protein from crude extracts of this bacterium in a sequence-specific and oxygen-dependent manner (19).…”

Mg‐chelatase of tobacco: identification of a Chl D cDNA sequence encoding a third subunit, analysis of the interaction of the three subunits with the yeast two‐hybrid system, and reconstitution of the enzyme activity by co‐expression of recombinant CHL D, CHL H and CHL I

“…The Mg-porphyrin branch starts with Mg-chelatase, which consists of at least three different subunits. The initial indication for several subunits was obtained after sequencing an ~45 kB genomic fragment of Rhodobacter capsulatus (Burke et al, 1993;Zsebo and Hearst, 1984) and Rhodobacter sphaeroides (Coomber et al, 1990) which contained genes involved in photosynthesis and pigment synthesis. Inactivation of three open reading frames in this gene cluster resulted in accumulating protoporphyrin IX in Rhodobacter capsulatus (Bollivar etaL, 1994b).…”